The body synthesizes vitamin d from cholesterol. I’ve read somewhere that some people have cholesterol levels so low that their body’s ability to produce vitamin d when exposed to sunlight can be significantly impaired. You don’t mention your cholesterol level in your comment, but if is very low, this issue might be worth exploring. We’ve all had “high cholesterol bad, low cholesterol good” drilled into our thoughts for so long that it’s easy to lose sight of the fact that cholesterol can be TOO low.
Interesting. I’ll look into that. I didn’t really study the cholesterol numbers because the doctor just said they were “very good”... which may mean exactly what you were talking about.